Transformers are used in electronic devices for providing power to the electronic devices. In conventional technology, power is transferred from the primary side of a transformer to an output circuit of the secondary side of the transformer mainly by means of resonance. More specifically, after a boosting circuit boosts an input voltage to a preset voltage, a half bridge circuit constituted of two field effect transistors (FETs) controls the preset voltage to charge a capacitor, which is coupled to the transformer in series. The capacitor and the transformer form an LC resonant circuit. Power of the resonant circuit is transferred from the primary side to the secondary side by the transformer. After receiving the power, the secondary side transfers the power to a load via a rectifying diode.